This invention pertains to structural support systems for the core of a nuclear reactor and more particularly to such support systems which are subject to both thermal perturbations and radiation induced swelling; as with liquid metal fast breeder reactors (LMFBR).
The primary restraint on the design of the core support system for an LMFBR is that the system must accurately and predictably position the fuel assemblies while causing a negative overall power coefficient of reactivity. Such a design is particularly difficult to achieve since thermal perturbations and radiation induced swelling constantly change the positional relationship of the structural elements.
The prior art basically discloses two contrasting approaches to this problem. The first approach features a relatively loose core, to wit, one in which the fuel assemblies are allowed to bow and other structural elements are allowed to freely change their positional relationship. The operating characteristics of the reactor are then predictable on the basis of the ultimate positional relationship of the elements at operating temperature. The EBR-II nuclear reactor is an example of this approach. The second approach features a tight core which restricts bowing, of which Fermi is an example. However, these present designs preceded the recognition of the degree to which radiation induced swelling effects the positional relationship of the structural elements of the core and its support system, and accordingly, the above examples made insufficient allowance for the resulting problems.